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United States Patent |
6,038,484
|
Kuzma
|
March 14, 2000
|
Cochlear electrode with modiolar-hugging system including a flexible
positioner
Abstract
An electrode system includes (1) an electrode array, made in a straight or
curved shape, but made on a flexible carrier so that it can easily bend
within a curved body cavity, such as the cochlea; and (2) a flexible
positioner, typically molded in a curved shape from a silicone polymer so
as to make it easy to slide into the body cavity. Some embodiments may
further include an electrode guiding insert. Yet other embodiments include
only a flexible positioner adapted to fill space within a human cochlea so
as to force an electrode array against a modiolar wall of the cochlea.
Insertion of the electrode array is performed using one of two methods. A
first method involves first inserting the flexible positioner into the
scala tympani (one of the channels of the cochlea) to a desired depth,
which desired depth typically involves a rotation of about 360 degrees and
causes the positioner to rest against the outer or lateral wall of the
scala tympani, leaving an opening slightly larger than the cross-section
of the electrode array adjacent the inner wall of the scala tympani, and
then second inserting the electrode array into the opening defined by the
positioner and inner wall. The guiding insert may be used, in some
embodiments, to assist guiding the electrode array into this opening. A
second method of insertion involves first inserting an electrode array
into the scala tympani, and then second inserting the positioner into the
scala tympani so as to lie between the electrode array and the outer wall
of the scala tympani, thereby forcing the electrode array against the
inner wall of the scala tympani. Insertion of the positioner into scala
tympani after the electrode array has been at least partially inserted
therein further carries the electrode array deeper into the scala tympani
to a desired final position, and maintains it in that position.
Inventors:
|
Kuzma; Janusz A. (Englewood, CO)
|
Assignee:
|
Advanced Bionics Corporation (Sylmar, CA)
|
Appl. No.:
|
140034 |
Filed:
|
August 26, 1998 |
Current U.S. Class: |
607/137 |
Intern'l Class: |
A61N 001/05 |
Field of Search: |
607/136,137,55-57
600/585,379
606/129
|
References Cited
U.S. Patent Documents
4284085 | Aug., 1981 | Hansen et al. | 607/137.
|
4819647 | Apr., 1989 | Byers et al.
| |
4832051 | May., 1989 | Jarvik et al.
| |
4898183 | Feb., 1990 | Kuzma.
| |
5000194 | Mar., 1991 | van den Honert et al.
| |
5037497 | Aug., 1991 | Stypulkowski.
| |
5443493 | Aug., 1995 | Byers et al.
| |
5545219 | Aug., 1996 | Kuzma.
| |
5578084 | Nov., 1996 | Kuzma et al.
| |
5603726 | Feb., 1997 | Schulman et al.
| |
5645585 | Jul., 1997 | Kuzma.
| |
5649970 | Jul., 1997 | Loeb et al.
| |
5653742 | Aug., 1997 | Parker et al.
| |
5667514 | Sep., 1997 | Heller.
| |
Foreign Patent Documents |
9631087 | Mar., 1996 | WO.
| |
Primary Examiner: Kamm; William E.
Assistant Examiner: Evanisko; George R.
Attorney, Agent or Firm: Gold; Bryant R.
Parent Case Text
This application claims the benefit of the following U.S. Provisional
patent applications: Ser. No. 60/087,655, filed Jun. 2, 1998; Ser. No.
60/079,676, filed Mar. 27, 1998; Ser. No. 60/067,534, filed Dec. 4, 1997;
Ser. No. 60/061,945, filed Oct. 14, 1997; and Ser. No. 60/056,055, filed
Sep. 2, 1997; all of which patent applications are incorporated herein by
reference.
Claims
What is claimed is:
1. An electrode system adapted for use with a tissue stimulation device
comprising:
a flexible electrode array having a multiplicity of electrode contacts
along one surface thereof;
a flexible positioner adapted for insertion into a body cavity, said
flexible positioner having front and rear sides, said body cavity having
front and back walls, said flexible positioner being adapted for insertion
into the body cavity so that the positioner assumes a position within the
body cavity having its rear side lie against the back wall of the cavity,
and leaving an open channel between the front side of the positioner and
the front wall of the body cavity; and
an electrode-guiding insert adapted for insertion into the open channel
created between the front side of the positioner and the front wall of the
body cavity;
wherein the flexible electrode array is insertable through the
electrode-guiding insert into the open channel so that the electrode
contacts are positioned adjacent the front wall of the body cavity.
2. The electrode system as set forth in claim 1 wherein the flexible
positioner is adapted for insertion within a human cochlea and comprises a
curved flexible positioner having a groove or channel running
longitudinally along its front side.
3. The electrode system as set forth in claim 1 wherein a distal portion of
the electrode array and a distal portion of the positioner each contain
engaging barbs adapted to interface with each other and secure the
electrode array in a desired position wherein the electrode contacts are
held against the front wall of the body cavity.
4. A flexible positioner for insertion into a body cavity, said flexible
positioner having front and rear sides, said body cavity having front and
back walls, said flexible positioner being adapted for insertion into the
body cavity so that the positioner assumes a position within the body
cavity having its rear side lie against the back wall of the cavity, and
leaving an open channel between the front side of the positioner and the
front wall of the body cavity, and wherein a tracing marker, having
properties that facilitate seeing the tracing marker on an imaging system,
is embedded in a distal end of the positioner.
5. The flexible positioner as set forth in claim 4 wherein the flexible
positioner comprises a curved flexible positioner having a side groove or
channel running longitudinally along its front side.
6. The flexible positioner as set forth in claim 5 wherein the positioner
is adapted to fill space within the body cavity along with an electrode
array, and wherein the positioner has a cross-sectional area sized such
that insertion of the positioner within the body cavity into which the
electrode array has already been at least partially inserted causes the
electrode array to be carried deeper into the body cavity by friction
created between engaging walls of the electrode array and positioner.
7. The flexible positioner as set forth in claim 4 wherein a distal portion
of the positioner has engaging barbs adapted to interface with other
engaging barbs of an electrode array positioned to reside within the side
groove of the positioner inside the body cavity.
8. The flexible positioner as set forth in claim 4 further including a
channel passing longitudinally through the positioner for removably
receiving a guiding stylet.
9. The flexible positioner as set forth in claim 8 wherein the channel is
sealed at its distal end.
10. An electrode system adapted for insertion into the scala tympani of a
human cochlea as part of a cochlear stimulation system, the electrode
system comprising:
a flexible electrode array having a multiplicity of electrode contacts, and
a flexible positioner adapted for use with the flexible electrode array,
said flexible positioner comprising an elongate, flexible body having
dimensions that facilitate its insertion fully into the scala tympani, the
scala tympani having front and back walls;
wherein the elongate flexible body of the positioner is made from a
silicone polymer formed in a generally curved shape, and the elongate
flexible body is separate and detached from the electrode array;
wherein the elongate flexible body of the positioner has a proximal end and
a distal end, and wherein the elongate flexible body is tapered, having a
larger cross sectional area at the proximal end than at the distal end,
and wherein, when inserted into the scala tympani, the flexible positioner
is adapted to assume a position within the scala tympani against the back
wall of the scala tympani; and
wherein the flexible electrode array is adapted to be inserted into the
scala tympani and positioned therein so that the flexible electrode array
lies between the positioner and the front wall of the scala tympani.
11. The electrode system of claim 10 wherein the elongate flexible body of
the positioner naturally assumes a shallow hook shape, wherein the distal
end of the positioner bends more than 90 degrees from a longitudinal axis
of the positioner at the proximal end.
12. The electrode system of claim 10 further including a hole passing
longitudinally through the elongate flexible body of the positioner from
its proximal end to its distal end.
13. The electrode system of claim 12 further including a smooth rounded
distal tip formed at the distal end of the positioner, wherein the smooth
rounded distal tip plugs the hole at the distal end of the positioner.
14. The electrode system of claim 12 further including a tracing marker
placed in the hole at the distal end of the positioner, and the smooth
rounded tip being formed on the distal side of the tracing marker, wherein
the smooth rounded tip plugs the hole at the distal end of the positioner.
15. The electrode system of claim 10 further including a side channel
formed along a front side of the positioner from the proximal end to the
distal end.
16. The electrode system of claim 10 further including a handle formed at
the proximal end of the positioner, the handle pointing in the same
direction as the curve formed in the positioner.
17. The electrode system of claim 10 wherein each of the multiplicity of
spaced-apart electrode contacts of the flexible electrode array lie along
a front surface of the electrode array, the front surface of the electrode
array comprising that surface nearest the front wall of the scala tympani
when the positioner and electrode array are inserted into the scala
tympani.
18. The electrode system of claim 17 wherein a distal portion of the
positioner has engaging barbs thereon, and a distal portion of the
electrode array also has engaging barbs thereon, the engaging barbs of the
positioner being adapted to detachably interface with the engaging barbs
of the electrode array when the positioner and electrode array combine to
form the electrode system.
Description
BACKGROUND OF THE INVENTION
The present invention relates to implantable stimulation devices, e.g.,
cochlear prosthesis used to electrically stimulate the auditory nerve, and
more particularly to an electrode array for use with a cochlear stimulator
that is designed to hug the modiolus so as to place electrode contacts of
the electrode array in close proximity to the ganglion cells and thereby
to the auditory nerve fibers.
Hearing loss, which may be due to many different causes, is generally of
two types: conductive and sensorineural. Of these, conductive hearing loss
occurs where the normal mechanical pathways for sound to reach the hair
cells in the cochlea are impeded, for example, by damage to the ossicles.
Conductive hearing loss may often be helped by use of conventional hearing
aids, which amplify sound so that acoustic information does reach the
cochlea and the hair cells. Some types of conductive hearing loss are also
amenable to alleviation by surgical procedures.
In many people who are profoundly deaf, however, the reason for their
deafness is sensorineural hearing loss. This type of hearing loss is due
to the absence or the destruction of the hair cells in the cochlea which
are needed to transduce acoustic signals into auditory nerve impulses.
These people are unable to derive any benefit from conventional hearing
aid systems, no matter how loud the acoustic stimulus is made, because
their mechanisms for transducing sound energy into auditory nerve impulses
have been damaged. Thus, in the absence of properly functioning hair
cells, there is no way auditory nerve impulses can be generated directly
from sounds.
To overcome sensorineural deafness, there have been developed numerous
cochlear implant systems--or cochlear prosthesis--which seek to bypass the
hair cells in the cochlear (the hair cells are located in the vicinity of
the radially outer wall of the cochlea) by presenting electrical
stimulation to the auditory nerve fibers directly, leading to the
perception of sound in the brain and an at least partial restoration of
hearing function. The common denominator in most of these cochlear
prosthesis systems has been the implantation into the cochlea of
electrodes which are responsive to a suitable external source of
electrical stimuli and which are intended to transmit those stimuli to the
ganglion cells and thereby to the auditory nerve fibers.
A cochlear prosthesis operates by direct electrical stimulation of the
auditory nerve cells, bypassing the defective cochlear hair cells that
normally transduce acoustic energy into electrical activity in such nerve
cells. In addition to stimulating the nerve cells, the electronic
circuitry and the electrode array of the cochlear prosthesis performs the
function of separating the acoustic signal into a number of parallel
channels of information, each representing the intensity of a narrow band
of frequencies within the acoustic spectrum. Ideally, each channel of
information would be conveyed selectively to the subset of auditory nerve
cells that normally transmitted information about that frequency band to
the brain. Those nerve cells are arranged in an orderly tonotopic
sequence, from high frequencies at the basal end of the cochlear spiral to
progressively lower frequencies towards the apex. In practice, this goal
tends to be difficult to realize because of the anatomy of the cochlea.
Over the past several years, a consensus has generally emerged that the
scala tympani, one of the three parallel ducts that, in parallel, make up
the spiral-shaped cochlea, provides the best location for implantation of
an electrode array used with a cochlear prosthesis. The electrode array to
be implanted in this site typically consists of a thin, elongated,
flexible carrier containing several longitudinally disposed and separately
connected stimulating electrode contacts, perhaps 6-30 in number. Such
electrode array is pushed into the scala tympani duct to a depth of about
20-30 mm via a surgical opening made in the round window at the basal end
of the duct. During use, electrical current is passed into the fluids and
tissues immediately surrounding the individual electrical contacts in
order to create transient potential gradients that, if sufficiently
strong, cause the nearby auditory nerve fibers to generate action
potentials. The auditory nerve fibers arise from cell bodies located in
the spiral ganglion, which lies in the bone, or modiolus, adjacent to the
scala tympani on the inside wall of its spiral course. Because the density
of electrical current flowing through volume conductors such as tissues
and fluids tends to be highest near the electrode contact that is the
source of such current, stimulation at one contact site tends to activate
selectively those spiral ganglion cells and their auditory nerve fibers
that are closest to that contact site. Thus, there is a need for the
electrode contacts to be positioned as close to the ganglion cells as
possible. This means, in practice, that the electrode array, after
implant, should preferably hug the modiolar wall, and that the individual
electrodes of the electrode array should be positioned on or near that
surface of the electrode array which is closest to the modiolar wall.
In order to address the above need, it is known in the art to make an
intracochlear electrode array that includes a spiral-shaped resilient
carrier which generally has a natural spiral shape so that it better
conforms to the shape of the scala tympani. See, e.g., U.S. Pat. No.
4,819,647. The '647 U.S. patent is incorporated herein by reference.
Unfortunately, while the electrode shown in the '647 patent represents a
significant advance in the art, there exists lack of sufficient shape
memory associated with the electrode to allow it to return to its original
curvature (once having been straightened for initial insertion) with
sufficient hugging force to allow it to wrap snugly against the modiolus
of the cochlea.
It is also known in the art, as shown in applicant's prior patents, U.S.
Pat. Nos. 5,545,219 and 5,645,585, to construct an electrode carrier from
two initially straight members, a rodlike electrode carrier and a flexible
rodlike positioning member. As shown in these patents, the two members
extend in substantially parallel relation to and closely alongside each
other, but are connected to each other only at their respective leading
and trailing end regions. After implant, a pushing force is applied to the
positioning member so that it is forced to assume an outwardly arched
configuration relative to the electrode carrier, thereby forcing the
electrode carrier into a close hugging engagement with the modiolus,
thereby placing the electrode contacts of the electrodes in as close a
juxtaposition to the cells of the spiral ganglion as possible. The '219
and '585 U.S. patents are also incorporated herein by reference.
Unfortunately, while the electrode array taught in the above-referenced
'219 and '585 patents has the right idea, i.e., to force the electrode
carrier into a close hugging engagement with the modiolus, it does so only
by use of an additional element that makes manufacture of the lead more
difficult and expensive, and only through application of an additional
pushing force which is applied to an electrode structure after it is
already fully inserted into the cochlea. Such additional pushing force may
easily cause damage to the delicate scala tympani. Moreover, the entire
electrode array may twist during the insertion process, or when the
additional pushing force is applied, thereby causing the electrode
contacts to twist and/or be forced away from the modiolus, rather than in
a hugging relationship therewith.
Thus, while it has long been known that an enhanced performance of a
cochlear implant can be achieved by proper placement of the electrode
contacts close to the modiolar wall of the cochlea, two main problems have
faced designers in attempting to achieve this goal. First, it is extremely
difficult to assemble electrode contacts on the medial side of the an
electrode array, facing the modiolus of the cochlea. Second, heretofore
there has either been the need for application of an external (and perhaps
unsafe) force, or a lack of sufficient shape memory, to allow the
electrode (after initial straightening to facilitate insertion) to assume
or return to the desired curvature needed to place the electrodes against
the modiolar wall so that the curvature wraps snugly around the modiolus
of the cochlea. As a result, the electrode contacts of the prior art
electrodes are generally positioned too far way from the modiolar wall.
It is thus evident that improvements are still needed in cochlear
electrodes, particularly to facilitate assembling an electrode so that the
electrode contacts are on the medial side of the electrode array, and to
better assure that the electrode assumes a close hugging relationship with
the modiolus once implantation of the electrode has occurred.
SUMMARY OF THE INVENTION
The present invention addresses the above and other needs by providing an
electrode system that allows for correct positioning of the electrode
contacts against the modiolar wall of the cochlea. Such "correct"
positioning is achieved through the use of an electrode system that
includes at least one of the following three main components: (1) an
electrode array, preferably made in a slightly curved shape, for improved
stability of electrode contact direction, made on a flexible carrier so
that it can easily bend within the cochlea; (2) a flexible positioner,
typically molded from a silicone polymer so as to make it easy to slide
into the cochlea, and made to assume a curved shape to facilitate its
insertion into the cochlea; and (3) an electrode guiding insert made from
a biocompatible material, such as platinum (Pt), titanium (Ti) or Teflon.
Insertion of the electrode array is performed in three main steps. First,
the flexible positioner is inserted through the appropriate dimension of
cochleostomy. This means it is inserted into the scala tympani (one of the
channels of the cochlea) to the desired depth. The desired depth typically
involves a rotation of about 360 degrees and causes the positioner to rest
against the outer or lateral wall of the scala tympani, leaving an opening
slightly larger than the cross-section of the electrode array adjacent the
inner wall of the scala tympani. Advantageously, the super-flexible nature
of the positioner prevents it from causing damage to the cochlear
structure. At the same time, once inserted, it provides a guide for the
electrode, and protects the cochlear walls from being damaged or touched
directly by the stiffer electrode body.
Second, after insertion of the positioner to the desired depth, the guiding
insert may be pushed into the opening of the cochlea.
Third, the electrode array is inserted through the opening of the guiding
insert to the desired depth. This desired depth is preferably beyond the
depth of the positioner. The distal end of the array advantageously
includes engaging or locking barbs that engage with corresponding barbs at
the distal end of the positioner. At this stage, the electrode is
positioned very close to the modiolus of the cochlea. Then, as a final
optimization of the position of the electrode contacts of the electrode
array, the electrode array is pulled back slightly (about 2 mm). This
backward motion assures that the distal tips of the electrode array and
the positioner are engaged by the barbs located thereon. Such engagement
may further serve to force the electrodes into direct contact with the
modiolar wall.
Advantageously, the electrode system of the present invention achieves the
following goals: (1) it virtually guarantees that the electrode array will
be optimally positioned against the modiolar wall in a cochlea of any
size; (2) the insertion of the electrode array avoids or produces minimal
trauma to the cochlear structure; (3) it allows deep insertion beyond 360
degrees; (4) it can be manufactured using easy, low cost technology; and
(5) the electrode can be easily removed and reinserted, if required.
In accordance with an alternate embodiment of the invention, there is
provided an electrode positioner that may be used with almost any
electrode array that is to be inserted into the cochlea in order to assure
that a desired modiolar-hugging position is achieved with the electrode
contacts of the array.
In accordance with yet an additional embodiment of the invention, a
cochlear electrode system is provided that includes (1) an electrode array
and (2) an electrode positioner. Using a preferred insertion technique or
method, the electrode array is first inserted into the cochlea as far as
it reasonably can be; then the positioner is inserted into the cochlea,
behind the electrode array so as to force or push the electrode contacts
of the array against the modiolar wall. Moreover, as the positioner is
thus inserted into the cochlea behind the electrode array, the positioner
carries the electrode deeper into the cochlea, e.g., approximately 1/2
turn deeper. In such instance, the positioner need not be equipped with
internal barbs at its distal end.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features and advantages of the present invention will
be more apparent from the following more particular description thereof,
presented in conjunction with the following drawings wherein:
FIGS. 1A and 1B show a side and cross-sectional view, respectively, of an
electrode array which forms part of the electrode system of the present
invention;
FIG. 1C illustrates an enlarged view of the engaging barbs used at a distal
end of the electrode array shown in FIG. 1A;
FIGS. 2A and 2B show a side and cross-sectional view, respectively, of a
curved positioner that forms part of the electrode system of the present
invention;
FIG. 2C depicts an enlarged view of a distal end of the positioner shown in
FIG. 2A;
FIGS. 3A, 3B and 3C illustrate a cross-sectional, top, and perspective
view, respectively, of an insert that forms part of the electrode system
of the present invention, which insert is used to guide the electrode as
it is inserted into the cochlea;
FIG. 4A illustrates insertion of the curved positioner into the scala
tympani of the cochlea;
FIG. 4B shows a cross-sectional view of the cochlea with the positioner
placed within the scala tympani;
FIG. 5 shows a schematic representation of the spiraling scala tympani of
the cochlea with the positioner inserted therein, and further illustrates
the placement of the electrode-guiding insert into the front opening of
the scala tympani;
FIG. 6A is a schematic representation of the cochlea as in FIG. 5, but with
the electrode array having been inserted into the scala tympani through
the electrode-guiding insert;
FIG. 6B is a cross-sectional view of the scala tympani of FIG. 6A, showing
the manner in which the positioner forces the electrode array to hug the
modiolus of the cochlea;
FIG. 7A depicts a preferred manner of making a multi-electrode electrode
array of the type shown in FIG. 1A;
FIG. 7B shows an enlarged view of the electrode contacts of the array of
FIG. 1A;
FIGS. 8A, 8B, 8C and 8D illustrate one manner in which wires may be bonded
to each of the electrode contacts of FIG. 7B during manufacture of the
electrode array;
FIG. 9 depicts a molding die onto which the partially-formed electrode
array of FIG. 7A, with wires attached to each of the electrodes as shown
in FIGS. 8A-8D, may be mounted in order to form a polymer carrier for the
electrode array;
FIG. 9A and 9B illustrate an alternative type of molding die onto which the
partially-formed electrode array of FIG. 7A, with wires attached to each
of the electrodes as shown in FIGS. 8A-8D, may be mounted in order to form
a polymer carrier for the electrode array;
FIG. 10 is a perspective view of a positioner made in accordance with the
present invention lying in a somewhat straightened position;
FIG. 11 is a schematic representation of the cochlea showing an alternate
technique for insertion of the electrode array, and in particular showing
the electrode array first inserted into the cochlea and showing the
positioner inserted second into the cochlea;
FIG. 11A is a sectional view taken along the line A--A of FIG. 11;
FIG. 12 is a schematic representation of the cochlea as in FIG. 11, but
showing the positioner fully inserted into the cochlea;
FIG. 12A is a sectional view of the cochlea taken along the line A--A of
FIG. 12;
FIG. 13 illustrates a side profile view of an alternative embodiment of a
positioner made in accordance with the invention;
FIG. 13A is a sectional view taken along the lines A--A of the positioner
of FIG. 13;
FIG. 13B is a sectional view taken along the line B--B of the positioner of
FIG. 13;
FIG. 13C is a sectional view taken along the line C--C of the positioner of
FIG. 13;
FIG. 13D is a sectional view taken along the line D--D of the positioner of
FIG. 13;
FIG. 14A is a view of the proximal end of the positioner of FIG. 13; and
FIG. 14B is a sectional view of the distal tip of the positioner of FIG. 13
.
Corresponding reference characters indicate corresponding components
throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE INVENTION
The following description is of the best mode presently contemplated for
carrying out the invention. This description is not to be taken in a
limiting sense, but is made merely for the purpose of describing the
general principles of the invention. The scope of the invention should be
determined with reference to the claims.
The invention described herein teaches one type of electrode system that
may be used with a cochlear stimulation system. Other electrodes and
electrode systems may also be used for this purpose as disclosed, e.g., in
Applicant's previously-filed patent applications Ser. No. 60/056,055,
filed Sep. 2, 1997, and Ser. No. 60/061,945, filed Oct. 14, 1997,
incorporated herein by reference. The materials, dimensions, methods of
manufacture, and the like, described in these prior-filed patent
applications are also applicable to the present invention.
Turning to FIGS. 1A and 1B, there is shown a side and a cross-sectional
view, respectively, of an electrode array 10 that forms part of an
electrode system 12 made in accordance with the present invention. The
cross-sectional view of FIG. 1B is taken along the line A--A of FIG. 1A. A
distal end portion 11 of the array 10 is shown in FIG. 1C.
As seen in FIGS. 1A, 1B and 1C, the electrode array 10 includes a plurality
of spaced-apart electrodes 200, formed within a flexible carrier 204. Each
of the electrodes is connected to at least one wire 202 which is embedded
within the carrier 204. A proximal end of the these wires 202 (not shown)
allows selective electrical connection to be made with each electrode 200
through use of a tissue stimulator, e.g., a cochlear stimulator.
As an important feature of the invention, in some embodiments, the distal
end portion 11 of the electrode array 10 includes a plurality of sloping
barbs or teeth 13. These barbs 13, as explained below, help maintain the
electrode array 10 in its desired position against the modiolus wall of
the cochlea once it is inserted into the cochlea.
A second component of the electrode system of the present invention is a
positioner 20, as illustrated in FIGS. 2A, 2B and 2C. FIG. 2A shows a side
view of the curved positioner 20. FIG. 2B shows an enlarged view of a
distal end portion 21 of the positioner 20, including a barb 23.
Typically, the distal end of the positioner 20 will include a plurality of
barbs 23 formed therein. FIG. 2C shows a cross-sectional view of the
positioner 20 taken along the line B--B of FIG. 2A. As seen in FIG. 2C,
the positioner 20 includes a shallow smooth groove or channel 25 located
along one side thereof. This channel or groove 25, as seen by the
dotted-line representation of the bottom of the channel in FIG. 2A,
traverses the entire length of the positioner 20.
The flexible positioner 20 is preferably made from a silicone polymer, and
may be molded to assume the curved shape shown in FIG. 2A, or it may be
molded to assume a more straightened shape. If curved, the radius of
curvature "R" is selected to be somewhat larger than the natural curvature
of the cochlea. That is, when inserted into the cochlea, the positioner 20
will have to assume a tighter wind or coil than that afforded by its
formed curved shape. This assures that when inserted into the cochlea, the
positioner 20 is held away from the modiolus wall, leaving a cavity or
channel against the modiolus wall wherein the electrode array may be
inserted.
A third component of the electrode system, in accordance with one
embodiment thereof, is an electrode-guide 30 as shown in FIGS. 3A, 3B and
3C. The guide 30 is designed to be inserted into the proximal end of the
cavity or channel formed between the modiolus wall and the grooved side of
the positioner 20. The guide 30 includes a sleeve portion 32 and a flange
portion 34. The sleeve portion 32 includes an opening or channel 31
therein having a size that allows the electrode array 10 (FIG. 1A, 1B) to
readily slide therethrough. A portion of the flange 34, as seen best in
FIG. 3B, is removed, thereby forming a straight edge 36 on one side of the
flange. As will be evident from FIG. 5, below, this removed portion of the
flange allows the insert 30 to fit snugly against the positioner 20 (i.e.,
the straight edge 36 fits up against the positioner 20) when the insert 30
is inserted into the cochlea.
The electrode-guiding insert 30 is made from a biocompatible material, such
as platinum (Pt), titanium (Ti) or Teflon.
In some embodiments, as described more fully below, the electrode-guiding
insert may be omitted.
Next, the method of using the electrode system of the present invention
will be described in connection with FIGS. 4A through 6B. First, as shown
in FIGS. 4A and 4B, the flexible positioner 20 is inserted into the scala
tympani (one of the channels of the cochlea) to the desired depth. The
desired depth typically involves a rotation of about 360 degrees and
causes, as seen best in FIG. 4B, the positioner 20 to rest against the
outer or lateral wall of the scala tympani. This position leaves a channel
or opening 22, one side of which is defined by the groove 25, adjacent the
inner wall (modiolus) of the scala tympani. The opening 22 is slightly
larger than the cross-section of the electrode array 10.
Advantageously, the super-flexible nature of the positioner prevents it
from causing damage to the cochlear structure. At the same time, once
inserted, the positioner 20 provides a guide for the electrode array 10,
and protects the cochlear walls from being damaged or touched directly by
the stiffer electrode body 204.
Once the positioner has been inserted to the desired depth, the
electrode-guiding insert 30 (if used) is pushed into the opening of the
channel 22. When this insertion is performed, the flat or straight side 36
of the flange 30 is placed against the grooved side of the positioner 20.
With the positioner 20 and electrode-guiding insert 30, in place, the
electrode array 10 is next inserted through the opening 31 of the guiding
insert 30 to the desired depth as shown in FIGS. 6A and 6B. Insertion is
performed so that the electrodes 200 lie on the inside curve of the
electrode array as it is inserted into the cochlea, thereby placing these
electrodes 300 adjacent the modiolus wall.
The desired depth of insertion is preferably beyond the depth of the
positioner 20. Advantageously, because the carrier body 204 of the
electrode array 10 is tapered, it can be sized so that the diameter of the
opening 31 within the guiding insert 30 effectively prevents further
insertion once full insertion has occurred.
As explained above, the distal end portion 11 of the electrode array 10
includes engaging or locking teeth or barbs 13 that engage with
corresponding teeth or barbs 23 located at the distal end of the
positioner. Once the electrode array 10 has been inserted, the electrodes
200 are positioned very close to the modiolus of the cochlea, as desired.
As a final optimization of the position of the electrode contacts 200 of
the electrode array, the electrode array 10 may be pulled back slightly
(about 2 mm). This backward motion assures that the distal end portions 11
and 21 of the electrode array and the positioner are engaged by the barbs
13 and 23 located thereon. Such engagement may further serve to force the
electrode contacts 200 into direct contact with the modiolar wall.
Turning next to FIGS. 7A through 9, a preferred method of making the
electrode array 10 will be described. It is to be emphasized that this
method of making the electrode array is not the only way an electrode
array suitable for use with the electrode system of the invention could be
made. Rather, it merely represents an easy and inexpensive (and thus a
preferred) way in which the electrode array may be fashioned.
Most designs of electrodes and connectors are based on the principle of
molding a contact or array of contacts, usually made from biocompatible
metal, into a polymer carrier like silicone or polyurethane rubber. The
electrode contacts are usually required to be located in a controlled
position in reference to the surface of the carrier, with specified
surface areas to be fully exposed to the stimulated or interconnection
area. Disadvantageously, making such electrodes or connectors becomes
extremely difficult, especially when the contacts are very small and/or a
large number of contacts are required, e.g., as is the case with a cochlea
electrode. The main problem encountered in the fabrication of such
electrodes or connectors is to find a reliable method of holding the
system of contacts in the desired and stable position during the process
of welding the connecting wires and molding the polymer carrier. A further
problem relates to maintaining a controlled surface of the contacts that
are to remain exposed, i.e., to ensure that the contacts are not covered
by the polymer when the carrier is molded.
The preferred methods of making the electrode array described below in
connection with FIG. 7A through FIG. 9B is based on the principle of
attaching (by the process of resistance welding) electrode contacts made
from precious, biocompatible material (such as platinum or its alloys) to
a foil carrier made from a non-toxic but chemically-active metal like iron
(Fe). Attached to the metal carrier, the electrode contacts remain in a
desired and stable position allowing easy connecting of the wiring system
and subsequent molding of the polymer carrier. After completion of the
molding process, the metal foil carrier is etched away using a mixture of
diluted acids, such as HNO.sub.3 and HCl. The precious metal contacts and
polymer are immune to the acid and remain in their intact, unaltered
shape, and thereby provide the desired electrode array structure.
To illustrate this method, the method will be described relative to the
fabrication of a multi-electrode electrode array suitable for insertion
into the cochlea. As a first step, an array of contacts 200 are welded
onto an iron carrier 100 so as to assume a desired spaced-apart
relationship, as shown in FIG. 7A. Each contact 200 consists of two pieces
of platinum foil 210 and 220, connected together and joined to the carrier
100 by a weld 230, as shown in FIG. 7B.
As a second step, a wiring system is connected to each of the electrode
contacts 200. This is accomplished as shown in FIGS. 8A, 8B, 8C and 8D. As
seen in FIG. 8B, for example, an insulated wire 202', having the
insulation removed from its tip, is laid on top of the electrode foil
pieces 210 and 220. One of the ends of the foil piece 220 is then folded
over to hold the end of the wire while the wire is welded or crimped in
position (FIG. 8B). Then, the other end of the foil 220 is folded over the
first folded end (FIG. 8C). If other wires are present, e.g., going to
electrode contacts further up the array, then such wires may pass over the
foil piece 210, lying parallel to the wire 202' so as to form a bundle of
wires 202. A similar bundle may be formed on the other side of the folded
foil piece 220, thereby forming another wire bundle 203. The ends of the
foil piece 210 may then be folded over the folded piece 220 (FIG. 8D) to
complete the wire system connection process.
Once the wire bundles 202 and 203 have been connected to the electrodes
200, the foil carrier 100 is placed on a molding die 300 as shown in FIG.
9. The die 300 has alignment pegs 310 adapted to align with corresponding
alignment holes 110 in the foil carrier 100. The die 300 further has a
cavity or channel 320 formed therein into which the required amount of
material to form the polymer carrier 204 (FIG. 1A) is injected. This
cavity or channel 320 may be shaped or formed as desired, e.g., to include
the teeth or barbs 23 described previously.
As an alternative to the flat-surface die 300 shown in FIG. 9, a curved die
301 may be used as shown in FIGS. 9A and 9B. Such die 301 includes a
curved surface 303 on which the foil carrier 100 may be placed. The die
301 has alignment pegs 311 adapted to align with corresponding alignment
holes 110 in the foil carrier 100. A channel or cavity 321 is formed in
the curved surface 303 into which the required amount of material to form
the polymer carrier is injected. By placing the foil carrier assembly 100
in the curved die of FIGS. 9A and 9B (note that FIG. 9A comprises a
perspective view of the die 301, and FIG. 9B comprises a side or profile
view of the die 301), the array can be molded or formed to assume a
lightly curved shape. Such slightly curved shape is preferred to achieve
directional stability of the array during insertion.
Thus, it is seen that through proper use of the suitable die 300 or 301, or
other dies, the electrode array may be made to assume a natural curved
shape, a slightly curved shape, or to be straight.
After the material cures, the foil carrier with the electrode array
assembly (which is now molded inside of the polymer) is removed from the
die 300 or 301 and placed in a mixture of diluted acids. The mixture of
diluted acids dissolves the foil carrier 100, thereby exposing a clean
surface of the electrode contacts 200. After washing to remove any residue
of acids and Fe salts, the main electrode array structure is completed.
Alternative Embodiments
Other embodiments of the invention may also be used. For example, the
positioner 20, shown in a somewhat straightened position in FIG. 10, may
be used with any type of electrode system or electrode array in order to
help position the electrode contacts of the array in a desired position
within the cochlea. When so used, the positioner may be inserted into the
cochlea first (i.e., before insertion of the electrode array), as
described above in connection with FIGS. 4A and 4B, or second (i.e., after
insertion of the electrode array), as described more fully below.
Typically, as indicated above, the positioner 20 is curved as illustrated
in FIGS. 2A, 2B and 2C, although the degree and amount of curvature is not
critical given the flexible nature of the positioner. The distal end of
the positioner 20 may include a plurality of barbs or bumps 23 formed
therein. Moreover, the positioner 20 includes a smooth groove or channel
25 located along one side thereof to facilitate holding the electrode
array 10 on that side of the positioner facing the modiolar wall. This
channel or groove 25 traverses the entire length of the positioner 20, or
at least the length of the positioner up to the distal tip where the barbs
or bumps 23 may be located.
As described above, the flexible positioner 20 is preferably made from a
silicone polymer, and is molded to assume a generally curved shape, with a
width or cross-sectional area that is tapered, as required, to match the
cross-sectional area or width of the cochlea. The radius of curvature "R"
is selected to be somewhat larger than the natural curvature of the
cochlea. That is, when inserted into the cochlea, the positioner 20 will
have to assume a tighter wind or coil than that afforded by its formed
curved shape. This assures that when inserted into the cochlea, the
positioner 20 is held away from the modiolus wall, leaving a cavity or
channel against the modiolus wall wherein the electrode array may be
inserted. Further, this preferred shape and positioning of the positioner
within the cochlea improve the directional stability of the electrode
array during insertion, i.e., help prevent rotation of the electrode
array, thereby assuring that the electrode contacts remain positioned
adjacent the modiolus wall.
One technique for inserting an electrode array 10 into the cochlea without
having to use a guiding insert 30 is to first insert the electrode array
10 into the cochlea using any desired technique, as shown in the FIG. 11.
Typically, during such insertion, the electrode contacts 200 of the
electrode array 10 will be oriented to face the desired wall within the
cochlea, e.g., the modiolar wall.
As evident from the schematic representation of FIG. 11, as well as the
sectional view of FIG. 11A, the electrode contacts 200 of the electrode
array 10, when the electrode array 10 is first inserted into the cochlea
are not firmly held in position against the inner wall (modiolus) of the
cochlea. In order to force or hold the electrode contacts up against the
modiolus, the positioner 20 is also inserted into the cochlea, behind the
electrode array 10, i.e., on the side of the electrode array 10 farthest
from the modiolus, as seen in FIG. 11 (which shows the distal tip 21 of
the positioner 20 just as it is first inserted behind the electrode array
10 within the cochlea).
As the positioner is pushed deeper into the cochlea, it forces the
electrode array 10 up against the modiolar wall, which action causes most,
if not all, of the electrode contacts 200 to be in direct contact
(touching) the modiolar wall. Moreover, as the positioner 20 is pushed
still deeper into the cochlea, it eventually grabs (either through a
friction fit, and/or with the assistance of the barbs or bumps 23) the
electrode array 10 and carries the electrode array 10 with it deeper into
the cochlea, causing the electrode array 10 to be inserted, e.g., an
additional 1/2 turn deeper into the cochlea than when initially inserted.
Advantageously, once in such fully inserted position, as shown in FIGS. 12
and 12A, the barbs or bumps 23 on the positioner, in combination with the
barbs or teeth 13 on the electrode array, prevent the electrode array 10
from sliding backwards out of the cochlea.
Note, typically the electrode array 10, as seen best in FIG. 1A, has an
offset 203. Such offset 203 functions as a stop to prevent the electrode
array from being inserted too deep into the cochlea. Even when such offset
cannot effectively function as a stop, it can always function as a mark,
to aid the physician to know when the desired insertion depth has been
achieved.
An alternative and preferred embodiment of a positioner 20' is illustrated
in FIGS. 13, 13A, 13B, 13C, 14A and 14B. As seen best in FIG. 13, the
positioner 20' assumes a general shallow hook shape. (Note, "shallow", in
this context, refers to the fact that a distal tip or end portion 21' of
the positioner bends only slightly more than 90 degrees from the
longitudinal axis or center line of the positioner at the proximal end.)
The distal end portion 21' is detailed in the sectional view of FIG. 14B.
The positioner 20' includes a channel or hole 27 for receiving a guiding
wire stylet, as explained below, that passes longitudinally through the
entire length of the body of the positioner. At the distal tip 21' as seen
best in FIG. 14B, a tracing marker 29 is embedded within the channel 27.
Such marker 29 is preferably made from platinum or other suitable material
that can be easily seen in X-ray or other images. A plug 27' is placed on
the proximal side of the marker 29, and a smooth rounded distal tip 21" is
formed on the distal side of the marker 29. The marker 29 advantageously
facilitates viewing of the location of the positioner using X-rays or
other imaging equipment.
A side channel 25 is formed along one side of the positioner body along its
entire length, as previously described in connection with the positioner
shown in FIG. 10. The positioner 20' is preferably tapered, as illustrated
generally in the sectional views of FIGS. 13A, 13B, 13C, and 13D taken
respectively at the lines A--A, B--B, C--C and D--D of FIG. 13.
Typical dimensions of a cochlear positioner made in accordance with this
preferred embodiment of the invention are shown in FIGS. 13, 13A, 13B,
13C, 14A and 14B, expressed in millimeters (mm) . As seen in these
figures, the channel 25 maintains the same approximate width of 1.00 mm
along the entire length of the positioner, even though the overall width
of the positioner tapers from about 1.50 mm by 1.30 mm at the proximal
end, to about 1.00 mm by 0.93 mm at the distal tip 21'. The stylet channel
27 has a diameter of approximately 0.3 mm.
The positioner 20' is made using a suitable mold, similar to that used in
making the electrode shown in FIG. 9A, on which a silastic tube, having an
inner diameter of 0.3 mm and an outer diameter of about 0.64 mm, is
placed. The body of the positioner 20' is then formed around the tube
using silicone or other suitable silastic material using molding
techniques known in the art. The tube passes through the entire length of
the positioner 20'. If necessary, the molding process may be carried out
in two steps, forming one half of the positioner body on one side of the
tube during a first step, and forming the other half of the positioner
body on the other side of the tube during a second step. The side channel
25 is formed along one side of the positioner during the molding process.
After the positioner has been formed as described above, a drop of
silastic, or other suitable material, is placed in the distal end of the
tube, followed by insertion of the tracking marker 29. The drop of
silastic forms the plug 27'. The tracking marker 29 is inserted into the
distal end of the tube sufficiently far so that additional silastic
material may be inserted into the tube and attach to the walls of the
positioner body at the distal end 21' so as to form a smooth rounded
distal tip 21" of the positioner.
A handle 24 is formed at the proximal end of the positioner, as seen in
FIGS. 13 and 14A. This handle 24 not only provides a suitable finger-hold
for grabbing hold of the positioner during the insertion process, but also
provides a visual indication of the orientation of the positioner because
the handle 24 points in the same direction as the curved distal tip 21'.
The embodiment of the positioner 20' shown in FIG. 13 advantageously
facilitates insertion of the positioner into the scala tympani duct of the
cochlea. As needed, an insertion tool, such as that described in U.S.
patent application Ser. No. 60/087,655, filed Jun. 2, 1998, may be used to
aid in the insertion process. If so, the handle 24 facilitates loading of
the positioner within the insertion tool, and further assures that the
positioner does not twist as it is inserted. The referenced patent
application, Ser. No. 60/087,655, is incorporated herein by reference.
During the insertion process, a wire stylet may be inserted into and
through the channel 27 until the distal tip of the stylet engages the plug
27'. Such insertion of the stylet will cause the distal portion of the
positioner to straighten, which in turn facilitates beginning or starting
the insertion process of the positioner into the open end of the scala
tympani duct of the cochlea. As the distal end portion 21' of the
positioner is inserted deeper into the scala tympani duct, the stylet may
be retracted, as needed. Further, as the insertion occurs, the position or
location of the distal tip of the positioner may be monitored on an X-ray
or other suitable imaging device by monitoring the location of the tracing
marker 29 as such marker readily shows up on the image displayed by the
X-ray or other imaging device.
As described above, it is thus seen that an electrode system is provided
wherein engagement of the tips of the electrode array 10 and positioner 20
or 20' by the internal friction of both components against the cochlear
walls, stabilizes the electrode contacts in the desired and optimal
position in direct contact with the modiolar wall. In some embodiments,
such positioning may be aided by the barbs 13 and 23 of the array and
positioner, respectively. In other embodiments, such barbs are not needed.
In a preferred embodiment, the positioner includes a channel 27 into which
a stylet may be removably inserted, and the location of the positioner
within the cochlear may be readily tracked by inclusion of a tracking
marker 29, made from, e.g., platinum, which is embedded within the distal
tip 21' of the positioner.
While the invention herein disclosed has been described by means of
specific embodiments and applications thereof, numerous modifications and
variations could be made thereto by those skilled in the art without
departing from the scope of the invention set forth in the claims.
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